U.S. Potatoes Could Get Disease Resistance from Their Mexican Cousins

The great American spud has a wild Mexican cousin with genes to help U.S. farmers cut their use of fungicides to combat late blight, the disease that caused the Irish potato famine. Agricultural Research Service researchers in Madison, Wis., have developed new ways to incorporate late blight resistance into U.S. potatoes from Solanum pinnatisectum, a wild species found in central Mexico.

Late blight, caused by the fungus Phytophthora infestans, costs potato growers about $3 billion annually worldwide, according to the International Potato Center (CIP) in Lima, Peru. In the United States, using fungicides to control late blight has driven potato production costs up to nearly $200 an acre in some potato-producing states.

Using a technique known as embryo rescue, the researchers mated S. pinnatisectum with a derivative of a commercial U.S. potato. Embryo rescue involves removing the normally developing embryo from the failing, developing seed and placing it on a culture media that will sustain its growth. A hybrid from the rescue can be used by breeders as a maternal parent in a mating with cultivated potatoes.

Until now, these wild Mexican species have been difficult to cross with most other cultivated or wild species. But its worth doing because the wild species have genetic resistance to viruses, insects, fungi and nematodes.

Another plus: This Mexican species resists early blight, which produces problems similar to late blight. Early blight is caused by the fungus Alternaria solani. In 1994, the annual cost for controlling early blight alone was estimated to be $21 to $44 million in the United States and Canada. Resistance to both blights is important to reduce reliance on fungicides. In trials, the hybrid also resisted the Colorado potato beetle.

The potato genetics work is part of a nationwide effort in horticultural research at ARS, the USDA's chief scientific agency. For more information, see the list of ARS national programs in "Crop Production, Product Value, and Safety" at: